Project Summary Pain control is a major challenge for physicians, who must ensure appropriate and effective pain control for their patients, while remaining mindful of the many negative effects of opioid dependence and addiction. Nowhere is there a more pressing need than in children and young adults, who are at high risk for drug abuse, and in post-operative care, since post-operative opioid use can be a starting point for long-term pain issues.1, 2 Postoperative pain control in the Nuss procedure, minimally invasive repair of the congenital chest wall deformity known as pectus excavatum, remains a significant problem for the 3000 patients who undergo this procedure each year, mostly adolescents and young adults.5-7 Many multimodal analgesic regimens have been tried, but optimal treatment remains unknown.6, 7-10, 25, 37-41 We propose to test a novel and promising strategy of using intra-operative cryoanalgesia during the Nuss procedure. Cryoanalgesia is the localized freezing of peripheral nerves through application of a cryoprobe, which quickly cools to temperatures of -50 to -70 C. This causes nerve axons to degenerate, temporarily preventing pain transmission. The fibrous outer neural structures remain intact, which facilitates complete axonal regeneration by approximately 4-6 weeks.11-15 The proposed study is a 20-subject prospective, randomized pilot trial comparing cryoanalgesia to thoracic epidural analgesia for post-operative pain control in patients undergoing the Nuss procedure. Subjects will be recruited from patients already scheduled for a Nuss procedure at our institution, and will undergo 1:1 randomization to either cryoanalgesia or thoracic epidural analgesia for perioperative pain control. During their hospitalization, patients' opiate usage will be prospectively recorded, and pain will be assessed twice per day. Upon discharge, patients will maintain a log of their opiate use, and will return to clinic at 2 weeks, 1 month, 3 months, and 1 year after Nuss procedure for post-operative assessment. Primary outcome is length of perioperative hospitalization, an objective measure that synthesizes many different aspects of a procedure and its subsequent post-operative course, including pain control. Secondary outcomes are post-operative narcotic usage and direct cost of perioperative hospitalization. Side effects of both interventions will also be assessed. This would be the first systematic investigation of cryoanalgesia for local nerve block in a thoracoscopic procedure, and the first study involving its use in adolescents and young adults. The results would have direct application for those undergoing the Nuss procedure to repair pectus excavatum. We will also delineate a reproducible protocol for delivering cryoanalgesia thoracoscopically, to ensure others can safely and effectively use this method if it proves beneficial. Although the focus is on the small subset of patients who undergo the Nuss procedure, if a standardized approach to cryoanalgesia delivery in a thoracoscopic procedure has a positive effect on patient outcomes and cost of hospitalization, the technique could be applied to a variety of surgical procedures, as well as for other neuropathic pain.